It is always important to inform any doctor you see of all medications you are taking, including any herbal or over-the-counter supplements. Although many medications can be taken concurrently, the potential for reactions exists between many medications as well; thus consideration must be given for this.
Sometimes the potential reaction is minimal and may be due to additive side effects (e.g., sedating effects may com-bine). Other times, the presence of one medication can influence the elimination of the other medicine from the body, either allowing excessive accumulation or causing too rapid a depletion.
Consequences can thus be toxicity or a lack of efficacy. The SSRIs are metabolized by specific liver enzyme groups that eliminate the medication. Each SSRI has a slightly different profile as to the enzymes involved in its own metabolism.
MAOIs are generally contraindicated in combination with all other antidepressants because of the risk for serotonin syndrome, which can be fatal (although there are certain combinations that skilled clinicians can prescribe in a methodical way to minimize the risks).
Serotonin syndrome occurs when an excess of serotonin exists in the central nervous system. Symptoms include tremor, confusion, incoordination, sweating, shivering, and agitation. Most SSRIs are contraindicated in combination with thioridazine (Mellaril) as well because of a risk of cardiac toxicity .
SSRIs should be used cautiously in combination with sibutramine (Imitrex), commonly prescribed for migraine, because of a risk for serotonin syndrome.
St. John’s wort, an herbal preparation used for depression, should be avoided when on a prescribed antidepressant, also because of a potential risk for serotonin syndrome.
Again, there are some circumstances when a psychiatrist will combine two SSRIs or an MAOI with a TCA, for example, but this is typically done cautiously and under his or her guidance.
As described in Question 42, MAOIs have very specific guidelines on foods to be avoided (see Table 4). Like-wise, MAOIs can have significant interactions with other medications. As noted previously here, they are not to be combined with most other antidepressants. In fact, MAOIs have to be discontinued 2 weeks before a trial of another antidepressant, or the other antidepressant is to be discontinued for 2 weeks before initiating an MAOI (5 weeks for fluoxetine).
There are many over-the-counter medications to be avoided, such as pseudoephedrine and oxymetazoline; thus it is important to check with your doctor and pharmacist before taking an over-the-counter medication while on an MAOI. This is sound policy with all medications, not just psychotropics.