Botox® & Dysport can indeed be used to treat stiff muscles, especially neck spasms. It will provide relief, but it is only treating the symptom though, and not the cause.
In my opinion it would be better to find the cause and correct it. There may be many reasons why you have constant neck spasms, and solving the problem is the only thing that will bring long term relief. A common cause of chronic neck or back pain is Fibromyalgia, often caused by long term stress and adrenal fatigue. Fibromyalgia leads to inflammation in the muscles, causing chronic pain and stiffness. Treating the adrenal fatigue effectively will stop these inflammatory processes in the muscles and provide long term relief.
Health Renewal also offers Biopuncture to treat muscle spasms and stiffness. With Biopuncture we inject homeopathic anti-inflammatories into the muscle knots in order to break them up, providing effective relief. If possible make an appointment with a Health Renewal doctor to discuss your case and to find the best possible solution for your health condition.