5htp and L-theanine are natural options. 5htp is precursor to serotonin and has similar impact as a SSRI without the side effects but should not be take long term. l-theanine (suntheanine trademark) is a GABA agonist so works similar to drugs such as Ativan which are prescribed for anxiety. l-theanine can be taken indefinitely without any side effects but it is not as effective as other GABA agonist drugs such as Ativan. Tenex can be effective as well but have side effects. Do your research and consult with your naturopath or doctor.

starting out applying only a tiny amount if you do, since new smells can cause/trigger sensory overloads.

Lavender and other oils can be found at chiropractors. lavender is natural, it reduces anxiety and is a natural antihistamine. I have heard of it being applied to the child's wrists, some parents even put it on a cotton ball and the child wares it around on a necklace. I think the skin application is safer, depending on the severity of autism. It should come with instructions on how much to use.

My son has been on Tenex for several years but it was prescribed to help with some of the ADHD-like symptoms such as lack of focus and concentration. It is a very small dose and he has not experienced any side effects.