Hundreds of thousands of people are estimated to get their prescriptions privately through online pharmacies.
Weight-loss jabs, known as GLP-1 receptor agonists, work by reducing food cravings.
The NPA has previously urged patients to avoid buying weight loss injections from unregulated online sellers, who may be selling fake drugs.
A person’s medical history should also be examined before sellers decide whether or not to dispense a weight-loss injection, and regular reviews must take place, it added.
Ashley Cohen of the National Pharmacy Association said that while the weight loss jabs are meant for people with a BMI of 30 or more, increasing numbers of the “worried well” are seeking them out as a “lifestyle” medication.
Speaking on BBC Breakfast, Mr Cohen warned that the injections can have serious side-effects, including stomach upsets, nausea and gallstones.