Chocolate and onion-syrup against cough

Cough serves a useful purpose if it is productive, i.e. if it removes excessive mucus from the airways. However, unproductive cough can be problematic, especially since there seems to be no safe cough medication for children; many of the over-the-counter drugs for treating cough in children have been banned due to their serious side effects. On the search for safe alternatives, I came across commonly used food items which effectively suppress cough and dilate the airways (chocolate) and which (presumably) help against respiratory tract infections (honey and onion).

Chocolate
Theobromine is used as an effective anti-tussative agent and as a brochodilator (Usmani 2005, Simons 1985). Therefore it should be possible to achieve the same cough-suppressing effect by consuming cocoa or chocolate. A typical dose of theobromine is 500-1000 mg (i.e. about 10 mg/kg). The theobromine content of cocoa varies between 0.5% and 2.7%. In order to get into the therapeutic range, my son (16 kg) would have to eat about 200 mg of theobromine. The maximal cocoa content he tolerates in chocolate is 85% (which is quite surprising, but since I hardly eat anything below 70% cocoa content he got used to it early on). So he needs to eat about 10-20 grams of very dark chocolate. Children metabolize theobromine quite fast, so the effect is not very long-lasting. My son has agreed to test this and it seems to work.

Honey-onion syrup
The other remedy against cough is onion syrup. I take an onion. I prefer red ones as they are not as hot as the white ones. I cut it into very small pieces (cubes of 1-2 mm length) and then I mix them with about the same amount of crystalline, good-quality honey. After a a few hours the mixture becomes liquid as the sugar pulls out the water from the plant cells (osmosis). Then I squeeze out the juice from the mix. One onion per day is the approximate dosage for respiratory tract infections. Honey and onion contain both anti-bacterial compounds, but I haven't found any good studies showing that this mix really helps. However, unlike the chocolate, this is an old, traditional recipe against cough.