It often takes two to four weeks for antidepressants to start having an effect, and six to12 weeks for antidepressants to have their full effect. The first antidepressant medications were introduced in the 1950s. Research has shown that imbalances in neurotransmitters like serotonin, dopamine, and norepinephrine can be corrected with antidepressants. Four groups of antidepressant medications are most often prescribed for depression:
- Selective serotonin reuptake inhibitors (SSRIs) act specifically on the neurotransmitter serotonin. They are the most common agents prescribed for depression worldwide. These agents block the reuptake of serotonin from the synapse to the nerve, thus artificially increasing the serotonin that is available in the synapse (this is functional serotonin, since it can become involved in signal transmission, the cardinal function of neurotransmitters). SSRIs include fluoxetine (Prozac), sertraline (Zoloft), paroxetine (Paxil), citalopram (Celexa), escitalopram (Lexapro) and fluvoxamine (Luvox).
- Serotonin and norepinephrine reuptake inhibitors (SNRIs) are the second-most popular antidepressants worldwide. These agents block the reuptake of both serotonin and norepinephrine from the synapse into the nerve (thus increasing the amounts of these chemicals that can participate in signal transmission). SNRIs include venlafaxine (Effexor) and duloxetine (Cymbalta).
- Bupropion (Wellbutrin) is a popular antidepressant medication classified as a norepinephrine-dopamine reuptake inhibitor (NDRI). It acts by blocking the reuptake of dopamine and norepinephrine.
- Mirtazapine (Remeron) works differently from the compounds discussed above. Mirtazapine targets specific serotonin and norepinephrine receptors in the brain, thus indirectly increasing the activity of several brain circuits.
- Tricyclic antidepressants (TCAs) are older agents used as first-line treatment. They work similarly to the SNRIs, but have other neurochemical properties result in side effect rates, as compared to almost all other antidepressants. They are sometimes used in cases where other antidepressants have not worked. TCAs include amitriptyline (Elavil, Limbitrol), desipramine (Norpramin), doxepin (Sinequan), imipramine (Norpramin, Tofranil), nortriptyline (Pamelor, Aventyl) and protriptyline (Vivactil).
- Monoamine oxidase inhibitors (MAOIs) are used. They work by inactivating enzymes in the brain which catabolize (chew up) serotonin, norepinephrine and dopamine from the synapse, thus increasing the levels of these chemicals in the brain. They can sometimes be effective for people who do not respond to other medications or who have “atypical” depression with marked anxiety, excessive sleeping, irritability, hypochondria or phobic characteristics. They have important medication interactions and require adherence to a particular diet. MAOIs include phenelzine (Nardil), isocarboxazid (Marplan) and tranylcypromine sulfate (Parnate).
- Non-antidepressant adjunctive agents. Often psychiatrists will combine the antidepressants mentioned above with each other (a “combination”) or with agents which are not antidepressants themselves (“augmentation”). These latter agents can include the atypical antipsychotic agents [aripiprazole (Abilify), olanzapine (Zyprexa), quetiapine (Seroquel), ziprasidone (Geodon), risperidone (Risperdal)], buspirone (Buspar), thyroid hormone (triiodothyonine or “T3”), the stimulants [methylphenidate (Ritalin), dextroaphetamine (Aderall)], dopamine receptor agonists [pramipexole (Mirapex), ropinirole (Requipp)], lithium, lamotrigine (Lamictal), s-adenosyl methionine (SAMe), pindolol and steroid hormones (testosterone, estrogen, DHEA).
Individuals and their families must be cautious during the early stages of medication treatment because normal energy levels and the ability to take action often return before mood improves. At this time - when decisions are easier to make, but depression is still severe - the risk of suicide may temporarily increase.
What are the side effects of the medications used to treat depression?
Different medications produce different side effects, and people differ in the type and severity of side effect they experience. About 50 percent of people who take antidepressant medications experience some side effects, particularly during the first weeks of treatment. Side effects that are particularly bothersome can often be treated by changing the dose of the medication, switching to a different medication, or treating the side effect directly with additional medications. Rarely, serious side effects such as fainting, heart problems or seizure may occur, but they are almost always treatable.
- Tricyclic antidepressants (TCAs) cause side effects that include dry mouth, constipation, bladder problems, sexual problems, blurred vision, dizziness, drowsiness, skin rash and weight gain or loss.
- Monoamine oxidase inhibitors (MAOIs). Individuals taking MAOIs may have to be careful about eating certain smoked, fermented, or pickled foods, drinking certain beverages, or taking some medications because they can cause severe high blood pressure in combination with the medication. A range of other, less serious side effects occur including weight gain, constipation, dry mouth, dizziness, headache, drowsiness, insomnia and sexual side effects (problems with arousal or satisfaction).
- SSRIs, and SNRIs tend to have fewer and different side effects, such as nausea, nervousness, insomnia, diarrhea, rash, agitation or sexual side effects (problems with arousal or orgasm).
- Bupropion generally causes fewer common side effects than TCAs and MAOIs. Its side effects include restlessness, insomnia, headache or a worsening of preexisting migraine conditions, tremor, dry mouth, agitation, confusion, rapid heartbeat, dizziness, nausea, constipation, menstrual complaints and rash.