Effects of Antidepressants
Antidepressants may cause mild and often temporary side effects in some people, but they are usually not long–term. However, any unusual reactions or side effects that interfere with normal functioning should be reported to a doctor immediately.
The most common side effects associated with SSRIs and SNRIs include:
Headache–usually temporary and will subside.
Nausea–temporary and usually short–lived.
Insomnia and nervousness (trouble falling asleep or waking often during the night)–may occur during the first few weeks but often subside over time or if the dose is reduced.
Agitation (feeling jittery).
Sexual problems–both men and women can experience sexual problems including reduced sex drive, erectile dysfunction, delayed ejaculation, or inability to have an orgasm.
Tricyclic antidepressants also can cause side effects including:
Dry mouth-it is helpful to drink plenty of water, chew gum, and clean teeth daily.
Constipation-it is helpful to eat more bran cereals, prunes, fruits, and vegetables.
Bladder problems–emptying the bladder may be difficult, and the urine stream may not be as strong as usual. Older men with enlarged prostate conditions may be more affected. The doctor should be notified if it is painful to urinate.
Sexual problems–sexual functioning may change, and side effects are similar to those from SSRIs.
Blurred vision–often passes soon and usually will not require a new corrective lenses prescription.
Drowsiness during the day–usually passes soon, but driving or operating heavy machinery should be avoided while drowsiness occurs. The more sedating antidepressants are generally taken at bedtime to help sleep and minimize daytime drowsiness.

THERAPEUTIC EFFICACY
There is a large amount of research evaluating the potential therapeutic effects of antidepressants, whether through efficacy studies under experimental conditions (including randomized clinical trials) or through studies of "real world" effectiveness. A sufficient response to a drug is often defined as at least a 50% reduction in self-reported or observed symptoms, with a partial response often defined as at least a 25% reduction. The term remission indicates a virtual elimination of depression symptoms, albeit with the risk of a recurrence of symptoms or complete relapse. Full remission or recovery signifies a full sustained return to a "normal" psychological state with full functioning.
LONG-TERM USE
The therapeutic effects of antidepressants typically do not continue once the course of medication ends, resulting in a high rate of relapse. A recent meta-analysis of 31 placebo-controlled antidepressant trials, mostly limited to studies covering a period of one year, found that 18% of patients who had responded to an antidepressant relapsed while still taking it, compared to 41% whose antidepressant was switched for a placebo. The American Psychiatric Association guidelines advise four to five months of continuation treatment on an antidepressant following the resolution of symptoms. For patients with a history of depressive episodes, the British Association for Psychopharmacology's 2000 Guidelines for Treating Depressive Disorders with Antidepressants advise remaining on an antidepressant for at least six months and as long as five years or indefinitely.
Whether or not someone relapses after stopping an antidepressant does not appear to be related to the duration of prior treatment, however, and gradual loss of therapeutic benefit during the course also occurs. A strategy involving the use of pharmacotherapy in the treatment of the acute episode, followed by psychotherapy in its residual phase, has been suggested by some studies.
ANTIDEPRESSANT WITHDRAWAL
Antidepressant withdrawal is possible if you abruptly stop antidepressant therapy after taking the medication for an extended period — usually longer than six weeks. Signs and symptoms of antidepressant withdrawal are sometimes referred to as antidepressant discontinuation syndrome.
Signs and symptoms of antidepressant withdrawal may include:
Irritability
Anxiety
Sadness
Insomnia
Headaches
Dizziness
Fatigue
Nausea
To minimize the risk of antidepressant withdrawal, consult your doctor before you change the dosage or stop antidepressant therapy. Your doctor may recommend gradually tapering off the dosage for a number of weeks to allow your brain to adapt to the absence of the drug.  
It's important to note that adjustment doesn't mean addiction. Antidepressants aren't considered addictive substances. Addiction represents harmful, long-term chemical changes in the brain. These changes can lead to tolerance, physical dependence and uncontrollable cravings. Withdrawal from an addictive substance is a very different phenomenon from withdrawal from antidepressants — which are simply drugs designed to restore normal chemical balance in the brain.
Keep in mind that it's sometimes difficult to differentiate between withdrawal symptoms and re-emergence of depression after you stop taking an antidepressant. Keep your doctor informed of your signs and symptoms. If necessary, your doctor may recommend resuming antidepressant therapy.
SIDE EFFECTS OF ANTIDEPRESSANTS
Antidepressants often cause adverse effects, and difficulty tolerating these is the most common reason for discontinuing an effective medication.
Side effects of SSRIs include: nausea, diarrhea, agitation, headaches. Sexual side effects are also common with SSRIs, such as loss of libido, failure to reach orgasm and erectile dysfunction. Serotonin syndrome is also a worrying condition associated with the use of SSRIs.
Side effects of TCAs (tricyclic antidepressants): Fairly common side effects include dry mouth, blurred vision, drowsiness, dizziness, tremors, sexual problems, skin rash, and weight gain or loss.
Side effects of MAOIs (monoamine oxidase inhibitors): Rare side effects of MAOIs like phenelzine (Nardil) and tranylcypromine (Parnate) include hepatitis, heart attack, stroke, and seizures. Serotonin syndrome is a side effect of MAOIs when combined with certain medications.  MAO inhibitors can produce a potentially lethal hypertensive reaction if taken with foods that contain excessively high levels of tyramine, such as mature cheese, cured meats or yeast extracts. Likewise, lethal reactions to both prescription and over the counter medications have occurred. Patients undergoing therapy with MAO inhibiting medications are monitored closely by their prescribing physicians, who are consulted before taking an over the counter or prescribed medication. Such patients must also inform emergency room personnel and keep information with their identification indicating that they are on MAO inhibitors.  Although these reactions may be lethal, the total number of deaths due to interactions and dietary concerns is comparable to over-the-counter medications.
SUICIDE AND ANTIDEPRESSANTS
Although studies have shown that antidepressants are generally safe, in some cases children, adolescents and young adults ages 18 to 24 may have an increase in suicidal thoughts or behavior when taking antidepressants, especially in the first few weeks after starting an antidepressant or changing a dosage. Because of this risk, they must be closely monitored by loved ones, caregivers and health care providers while taking antidepressants. The Food and Drug Administration (FDA) now requires that all antidepressant medications carry a warning about suicide (The Food and Drug Administration requires Black Box warnings on all SSRIs, which state that they double suicidal rates (from 2 in 1,000 to 4 in 1,000) in children and adolescents. The increased risk for suicidality and suicidal behavior among adults under 25 approaches that seen in children and adolescents.). Patients with depression are at greatest risk for suicide immediately after treatment has begun, as antidepressants can reduce the symptoms of depression such as psychomotor retardation or lack of motivation before mood starts to improve.
Although this appears paradoxical, studies indicate that suicidal ideation is a relatively common at the start of antidepressant therapy, and it may be especially common in younger patients such as pre-adolescents and teenagers. Manufacturers and physicians often recommend that other family members and loved ones monitor the young patient's behavior for any signs of suicidal ideation or behaviors, especially in the first eight weeks of therapy.
Until the black box warnings on these drugs were issued by FDA and equivalent agencies in other nations, side effects and alerting families to risk were largely ignored and downplayed by manufacturers and practitioners. This may have resulted in some deaths by suicide although direct proof for such a link is largely anecdotal. The higher incidence of suicide ideation reported in a number of studies has drawn attention and caution in how these drugs are used.
People under the age of 24 who suffer from depression are warned that the use of antidepressants could increase the risk of suicidal thoughts and behaviour. Federal health officials unveiled proposed changes to the labels on antidepressant drugs in December 2006 to warn people of this danger.
On September 6, 2007, the Centers for Disease Control and Prevention reported that the suicide rate in American adolescents, (especially girls, 10 to 24 years old), increased 8% (2003 to 2004), the largest jump in 15 years, to 4,599 suicides in Americans ages 10 to 24 in 2004, from 4,232 in 2003, giving a suicide rate of 7.32 per 100,000 people that age. The rate previously dropped to 6.78 per 100,000 in 2003 from 9.48 per 100,000 in 1990. The findings reinforced the fact that antidepressant drugs reduce suicide risk. Psychiatrists found that the increase is due to the decline in prescriptions of antidepressant drugs like Prozac to young people since 2003, leaving more cases of serious depression untreated. In a December 2006 study, The American Journal of Psychiatry said that a decrease in antidepressant prescriptions to minors of just a few percentage points coincided with a 14 percent increase in suicides in the United States; in the Netherlands, the suicide rate was 50% up after a fall in antidepressant prescriptions. Critics of this study say that the US "2004 suicide figures were compared simplistically with the previous year, rather than examining the change in trends over several years". The pitfalls of such attempts to infer a trend using just two data points (years 2003 and 2004) are further demonstrated by the fact that, according to the new epidemiological data, the suicide rate in 2005 in children and adolescents actually declined despite the continuing decrease of SSRI prescriptions. "It is risky to draw conclusions from limited ecologic analyses of isolated year-to-year fluctuations in antidepressant prescriptions and suicides. One promising epidemiological approach involves examining the associations between trends in psychotropic medication use and suicide over time across a large number of small geographic regions. Until the results of more detailed analyses are known, prudence dictates deferring judgment concerning the public health effects of the FDA warnings."
SEXUAL SIDE EFFECTS OF ANTIDEPRESSANTS
Sexual side effects are common with antidepressants in both men and women.  The severity of sexual side effects depends on the individual and the specific type and dose of antidepressant. For some people, sexual side effects are minor or may ease up as their bodies adjust to the medication.  For others, sexual side effects continue to be a problem.
Antidepressants with the lowest rate of sexual side effects include:  
Bupropion (Wellbutrin)
Mirtazapine (Remeron)

Antidepressants most likely to cause sexual side effects include:
Selective serotonin reuptake inhibitors (SSRIs). These commonly prescribed antidepressants cause sexual side effects in most people. SSRIs include citalopram (Celexa), escitalopram (Lexapro), fluoxetine (Prozac, Prozac Weekly), fluvoxamine (Luvox), paroxetine (Paxil, Paxil CR) and sertraline (Zoloft). Fluvoxamine may cause less bothersome sexual side effects than other SSRIs.
Serotonin-norepinephrine reuptake inhibitors (SNRIs), which include venlafaxine (Effexor) and duloxetine (Cymbalta). The recently approved SNRI desvenlafaxine (Pristiq) may cause fewer sexual side effects than some other antidepressants, but more research is needed to confirm this.
Tricyclic and tetracyclic antidepressants, such as amitriptyline, clomipramine (Anafranil), amoxapine  and desipramine (Norpramin).
Monoamine oxidase inhibitors (MAOIs), such as isocarboxazid (Marplan), phenelzine (Nardil) and tranylcypromine (Parnate).

If you're taking an antidepressant that causes sexual side effects, one of these strategies may help:
Waiting several weeks to see whether sexual side effects get better.
Scheduling sexual activity before taking an antidepressant if your antidepressant requires a once-a-day dose.
Switching to another antidepressant that may be less likely to cause sexual side effects.
Adding a second antidepressant or another type of medication to counter sexual side effects. For example, the addition of the antidepressant bupropion (Wellbutrin) or the anti-anxiety medication buspirone (Buspar) may ease sexual side effects caused by an antidepressant.
Adding a medication to directly improve sexual function, such as sildenafil (Viagra), tadalafil (Cialis) or vardenafil (Levitra). Although these medications are used to treat sexual problems in men, initial research suggests sildenafil may also improve sexual problems caused by antidepressants in some women.
Stopping medication because of sexual side effects is a common problem, and for most people this means depression returns. Work with your doctor to find an effective antidepressant or combination of medications that will reduce your sexual side effects and keep your depression under control. Be patient. Because everyone reacts differently to antidepressants, it may take some trial and error to identify what works best for you.
Don't underestimate the importance of finding a medication with tolerable sexual side effects. Poor sexual function can cause depression; likewise, depression can worsen sexual function. For most people, sexual function is important for maintaining confidence and a satisfying relationship with their romantic partner.
MORE ABOUT SEXUAL DYSFUNCTION - THIS IS TOO TECHNICAL TO INCLUDE BUT MAY BE USED AS A REFERENCE WHEN DEVELOPING CONTENT
Sexual dysfunction is a very common side effect, especially with SSRIs. Common sexual side effects include problems with libido (sexual desire), lack of interest in sex, and anorgasmia (trouble achieving orgasm). Although usually reversible, these sexual side effects can, in rare cases, last for months or years after the drug has been completely withdrawn. This is known as Post SSRI Sexual Dysfunction.
SSRI-induced sexual dysfunction affects 30% to 50% or more of individuals who take these drugs for depression. Biochemical mechanisms suggested as causative include increased serotonin, particularly affecting 5HT2 and 5HT3 receptors; decreased dopamine; blockade of cholingeric and alpha-1 adrenergic receptors; inhibition of nitric oxide synthetase; and elevation of prolactin levels.
Bupropion, a dual reuptake inhibitor (NE and DA), often causes a moderate increase in libido, due to increased dopamine activity. This effect is also seen with dopamine reuptake inhibitors, CNS stimulants and dopamine agonists, and is due to increases in testosterone production (due to inhibition of prolactin) and nitric oxide synthesis. Mirtazapine (Remeron) is reported to have fewer sexual side effects, most likely because it antagonizes 5-HT2 and 5-HT3 receptors. Mirtazapine can in some cases reverse sexual dysfunction induced by SSRIs, which is also likely due to its antagonisation of 5-HT2 and 5-HT3 receptors
Apomorphine, nefazodone and nitroglycerin have been shown to reverse some sexual dysfunction via increased nitric oxide activity. MAOIs are reported to have fewer negative effects on sexual function and libido, particularly moclobemide at a 1.9% rate of occurrence. Bethanechol has been reported to reverse MAOI-induced sexual dysfunction via its cholinergic agonist properties.
EMOTION AND MOOD ISSUES (THYMOANESTHESIA) WITH ANTIDEPRESSANTS
Closely related to sexual side effects is the phenomenon of emotional blunting, or mood anesthesia. Many users of SSRIs complain of apathy, lack of motivation, emotional numbness, feelings of detachment, and indifference to surroundings. They may describe this as a feeling of "not caring about anything anymore." All SSRIs, SNRIs, and serotonergic TCAs can cause this to varying degrees, especially at high doses.
REM SLEEP AND ANTIDEPRESSANTS
All major antidepressant drugs, except trimipramine and mirtazapine, suppress REM sleep, and it has been proposed that the clinical efficacy of these drugs largely derives from their suppressant effects on REM sleep. The three major classes of antidepressant drugs, monoamine oxidase inhibitors (MAOIs), tricyclic antidepressants (TCAs) and selective serotonin reuptake inhibitors (SSRIs), profoundly suppress REM sleep. Mirtazapine either has no effect on REM sleep or increases it slightly. The MAOIs almost completely suppress REM sleep, while the TCAs and SSRIs have been shown to produce immediate (40-85%) and sustained (30-50%) reductions in REM sleep. This effect often causes increased fatigue in patients who take large doses of antidepressants for extended periods of time. Such fatigue can occasionally interfere with a patient's everyday activities. Abrupt discontinuation of MAOIs can cause a temporary phenomenon known as "REM rebound" in which the patient experiences extremely vivid dreams and nightmares.
WEIGHT GAIN
Many antidepressants are associated with weight gain usually in the range of 5–25 kg (11–55 lb) but rarely upwards of 50 kg (110 lb). The specific cause is unknown, but antidepressants are associated with increased cravings, an inability to feel full despite consuming enough calories, low energy levels and increased daytime sleepiness, which can lead to overeating and a lack of desire to exercise, and dry mouth, which can lead to ingestion of calorie-laden beverages. The antihistaminic properties of certain NaSSA and TCA class antidepressants have been shown to contribute to the common side effects of increased appetite and weight gain associated with these classes of medication. Eating low fat, low protein carbohydrate snacks and carbohydrate-rich dinners allows the brain to make serotonin which then controls appetite and balances mood. Carbohydrates thus eaten, as part of a balanced diet, by virtue of their effect on brain serotonin levels, can support weight loss in the setting of antidepressant weight gain.