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Tricyclics: Potential Side Effects
Another group of side effects arises from the impact of tricyclics on alpha 1 adrenergic receptors. By blocking these receptors, the drugs can increase heart rate and increase blood pressure. While both of these are relatively harmless in young, healthy patients, they are potentially fatal in patients with heart disease. In addition to these effects, the hypotension can lead to dizziness and injury in many patients. The change in heart rate is most pronounced in those drugs with secondary amine groups, such as desipramine. The impacts on the cardiovascular system make it easy to overdose on tricyclics. A week’s supply of them can be a fatal dose in many individuals, which is a serious worry because of the danger of suicide in depressed people.
The antihistaminic effects of tricyclics can include sedation and weight gain, though neither of these effects is well understood. Sedation is particularly seen in tertiary amine tricyclics, and weight gain is seen at particularly high levels in amitriptyline, and low levels with protriptyline and desipramine, which have stimulant properties. Weight gain can also be attributed to a carbohydrate craving experienced by users of tricyclic antidepressants, and a slowing of metabolism. Some impact on dopamine D2 receptors has also been observed, and may impair movement.
Caution must be taken when using tricyclic antidepressants in conjunction with several other drugs, particularly MAOIs, norepinephrine and epinephrine, and phenothiazines. By combining tricyclics with MAOIs, one might experience stroke, convulsions and even death, though this combination can be achieved safely, especially with a tertiary amine compound. Norepinephrine and epinephrine, used for various medical conditions, can cause enormous increases in blood pressure and other problematic cardiovascular conditions when combined with tricyclics. Phenothiazines can be cholinergically addictive in combination with tricyclics, though combining them may be necessary for delusional depression.
In addition, haloperidol and phenytoin can also have potentially fatal reactions with tricyclics.
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Tricyclic antidepressants boast a wide and disruptive range of side effects from dry mouth to potential toxicity. Dry mouth, one of the best-known effects, is one of many effects attributed to the effects of the drugs on muscarinic cholinergic receptors. By blocking these sites, they can cause blurred vision, constipation, urinary retention, cognitive functioning and may have some impact on sexual functioning. Confusion, memory impairment, and delirium have all been attributed to tricyclic use in geriatric patients. And while the majority of these effects only serve to annoy young, healthy patients, for older patients they can be life threatening. These effects are found in all tricyclics, because they all have significant antagonist properties at muscarinic cholinergic receptors.