There are no documented long-term effects of combining antidepressants and anti-anxiety drugs. Antidepressants are often used to treat anxiety disorders, and if those are ineffective, beta-blockers or benzodiazepines are prescribed, according to the National Institute of Mental Health. However, both beta-blockers and benzodiazepines are used as a short-term or as-needed treatment and are not prescribed long enough for long-term effects to present.
Most antidepressants work by increasing the amount of serotonin, norepinephrine or dopamine absorbed by the neurotransmitters in the brain, says the National Institute of Mental Health. Since these drugs change the chemical composition of the brain, they carry the risk of slowing down the central nervous system.
The combination of benzodiazepines or other short-term anti-anxiety drugs and antidepressants can be fatal because they further depress the central nervous system when taken together, raising the risk for overdose, according to Drugs.com. These same effects can also be caused by combining benzodiazepines with alcohol.
Some beta-blockers can be dangerous when taken with anti-psychotics, such as antidepressants, because they slow the heart and can lead to arrhythmia, notes the National Institute of Mental Health. However, since beta-blockers are not typically prescribed as a long-term treatment for anxiety disorders, the risk of arrhythmia is not a long-term effect of the combination of the drugs.