Some single person experiments includes “blinding” — making each treatment appear the same to reduce a psychological biases for or against each version. (Knowing that a treatment is newer or a stronger dosage can boost its perceived effectiveness by an average of 9% versus a control.)
Doctors can instruct a compounding pharmacist to create a double blind by putting different treatments or strengths (or a placebo) into identical pills or liquids. The bottles can be sequentially labelled (for example 1, 2, 3, 4, 5, 6) so that neither you or the doctor know which treatment you’re taking in a given time period.
Once the experiment is over, the pharmacist can provide a key that reveals which code corresponded to which treatment. (This might reveal, for example that you’d taken six successive weeks of A, B, B, A, A, and finally B.)
Particularly for nonpharmaceuticals, some people ask a friend to help with blinding by distributing different treatments into identical containers. This is simple for oils—for $6.99, you can buy 25 plastic dropper bottles or six glass dropper bottles. Funnels are available too. The same goes for ointments and creams—five jars cost $10 on Amazon.
The friend might label each as A, B, C, D, E, F (one for each treatment period using the schedule you pick) being careful to separately note which treatment went into each container, and then pass the containers over to you.
(Note that, historically, not all experiments include blinding, particularly when it’s impossible to create seemingly identical versions of each treatment, for example when a treatment involves obvious physical alterations.)