Compositions containing nicotine and/or nicotinic acetylcholine receptor agonists are provided for administration in therapeutically effective amounts to enhance muscle development in animals, the nicotine and/or nicotinic acetylcholine receptor agonists being particularly derived from natural sources that produce beneficially high amounts nicotine and/or nicotinic acetylcholine receptor agonists which is also well-tolerated and ingestible for the intended purpose.