I've done that plenty of times, including higher multiples. Usually with no effect. Cumin at something like 5 heaping tsps increased the duration from 3 days to 4, but no other effect I noticed, so I went back to a level tsp. I also usually try effective treatments at lower doses, to find the minimal one that works.How many tried doubling the dose I wonder?
As for doubling the dose, if you've bought a bottle of the stuff and it doesn't work at the recommended (for disorders other than ME) dosage, why wouldn't you try it at higher doses (unless there are obvious hazards)? You can't get a refund for the unused portion, and there's at least a chance that it might work at a higher dosage. I've also tried the "didn't work" treatments again later, in case something prevented them from working the first time, which is possible. Maybe it needs a cofactor, or there's a counterfactor (some foods block some drugs). If you've bought it, why not experiment in different ways.