I was told about the amazing medicinal qualities of wild lettuce recently, and my immediate vocal reaction was "that's interesting, I'll have to do a little research." What I didn't say out loud, but was thinking, was which species? As it turns out, my internal commentary was the bit I should have said out loud, because that's the important part... There are 50 species of wild lettuce, possibly more, and they grow in locations around the world. But the interwebs information on the possible pharmacological import of the 'wild lettuce' rarely differentiates between species, making it mostly useless. Because species is important, especially in such a diverse group of plants. Not all will possess the qualities attributed to it, some will be toxic, and others will be harmless (thank goodness). So... Lactuca sativa, which is found in the wild in places like Turkey, is the common everyday lettuce you find in the grocery here in America. I know I have readers worldwide, but as this conversation took place in the good old US of A, I'll direct the post mostly to this area. Lactuca canadensis is the common yellow-flowered wild lettuce of North America. Lactuca virosa, which grows wild in Europe and parts of the Middle East, and may be found in southern parts of the US as an invasive species, is the wild lettuce commonly believed to have medicinal properties.
Yesterday, Mom gave me a link to what WebMD has to say about it. If you'll note, there is no specific identification of which species, or indeed, how to identify the plant accurately.
What aren't you seeing there? You aren't seeing any actual scientific data. If you were to click onto the tabs at the top - which I'm going to guess most people don't do, you would find that it says there is insufficient evidence for any of these claims. I wonder how many would pay attention to the side effects? "Wild lettuce seems safe for most people in small amounts. Large amounts, however, can slow breathing and might cause death. Applying wild lettuce directly to the skin can cause irritation. Large amounts can cause sweating, fast heartbeat, pupil dilation, dizziness, ringing in the ears, vision changes, sedation, breathing difficulty, and death." So what is a small amount? A large amount? Those are quite vague terms, especially when it comes to drugs (and yes, this is a drug as it's being used here). The last tab over includes this: "At this time there is not enough scientific information to determine an appropriate range of doses for wild lettuce. Keep in mind that natural products are not always necessarily safe and dosages can be important."
Moving away from a popular 'medical' site, into actual studies done on the potential of the various wild lettuces, we find that no central analgesic (pain relief) effect is found from the seeds, although it is a common folk remedy in Turkey and surrounding areas. Despite the common name 'opium lettuce' and the ascription of properties similar to morphine to the wild lettuces, there is no opiate property seen on injection. As a matter of fact, as far back as the 1930s, scathing summaries of the lack of evidence for any opioid properties were available (but seem to have been ignored). The attribution of the opiate property seems to have been largely based on the smell, since the sap of the lettuce, collected and dried, seems to have smelled like that of the morphine poppy. Not a good basis for medicine. L. sativa (again, this is the domestic lettuce) stem extract was shown to have a sedative effect in toads. I'm not sure that toads are a good model organism for humans, but you should also note that high doses cause heart arrhythmia. There is insufficient evidence, however, to indicate that wild lettuce is useful for insomnia.
If you are interested in natural remedies, at a minimum, do more research into them than WebMD. I highly suggest trying Google Scholar to begin with, rather than the open Web. You'll get less (note I am not saying none!) of the flaky sites trying to sell you something. Try searching for paired terms like 'wild lettuce pharmokinetics' or 'wild lettuce toxicity' in order to find results specific to medicinal uses. When you do this, you'll find articles like this one, detailing the toxic effects of wild lettuce on three people who consumed it, fortunately with no long-lasting effects other than some time in the hospital being very ill. You might also find a large, very useful, review of many natural supplements and herbs, detailing their interactions with the human system and other drugs. This is important: any drugs have the potential to interact in bad ways with one another, and I'll remind you again, any substance you use for medicine, no matter if you picked it yourself, is a drug.
I am not saying 'don't do it!' what I am saying is 'proceed with caution.' Wild lettuce (L. canadensis) native to the Americas, is not shown to possess the active pharmaceutical ingredients of L. sativa or L. virosa (which means, by the way, toxic). It is known to be edible at some stages of development, so drinking it as a tea will probably not hurt in moderation. Probably... but be absolutely certain of your identification of the plant before you harvest. Do your due diligence to check for any interactions with any prescribed medicines, natural supplements, or other herbs you are taking, before consuming an unknown substance. Be sure to let your doctor know everything you are taking or using, not just the stuff in the bottles with a label. Wild lettuce can cause uncontrollable bleeding if taken incorrectly (see above review of supplements). It can also be toxic, taken in excess or at the wrong time of year. Self-medication is a dangerous road, so tread lightly. On the other hand, the placebo effect of the human mind is a strange and wondrous thing, so if you find relief, enjoy that. Just don't overdo it.