Welcome to HCM! I have had patients gain weight on Lymecycline (tetracycline) and report hair loss. May I suggest that you try reducing your sodium and carbohydrates (sugar,honey,fructose) to reduce the bloating? Sodium can be limited to 2300 mg which is equivalent to a teaspoon of salt (sodium + chloride). That may help reduce some of the 10 pounds you gained. There is also a possible vitamin B deficiency with long-term use, which may interact with weight. B12 deficiency despite not showing up in bloodwork may be a complication with longterm use of lymecycline and B12 affects metabolic syndrome, diabetes and many other bodily processes just now appearing in the literature. Take drug one hour before meals or two hours after and do not combine with any supplements. Other deficiencies noted with this drug are calcium, iron, magnesium and zinc - noted from Drug Nutrient Interaction Handbook 2015. Mechanism aside from bloating for weight gain is not known at this time. If you cut out the types of carbohydrates I mentioned, it may help with losing those last few pounds. I am making no recommendations for vitamin supplementation with the exception of vitamin B12. I hope this has answered your query. Feel free to visit me anytime. Kathryn Shattler, MS,RDN