Keeping your travel and medical insurance providers aware that you're on weight loss medication is very important, as not keeping them informed can mean you're not covered for issues or illnesses related to your treatment, and potentially could invalidate your cover when travelling.
Make sure you've informed your travel insurance or medical insurance provider once you have started the treatment, or when you're purchasing single trip travel insurance, to ensure you're fully covered whilst travelling - even if you're not taking the medication with you!