Yes, amitriptyline does cause weight gain in some people. This is a relatively common side effect, especially with long‑term use, and may be linked to increased appetite and improved mood.
Besides weight gain, other common side effects of amitriptyline include constipation, dry mouth, headache, dizziness, and drowsiness.
Although it is less common, amitriptyline can also cause more serious problems in some people, such as heart rhythm changes, urinary retention, or liver toxicity. For this reason, amitriptyline should only be taken as prescribed by a healthcare provider.