You should always talk to your health care practitioner before combining drugs and natural health products. Depending on the dosage taken, a natural health product can be just as potent as a drug. Therefore, when taken in combination with a medication, acting on the same target in the body, the combination can result in side effects.
Cymbalta is a selective serotonin and norepinephrine reuptake inhibitors (SSNRIs). Basically, it acts on chemicals like serotonin in the brain. California poppy acts on both opioid and serotonin receptors in the brain. Therefore, you theoretically expect an additive type interaction if you take both Cymbalta and California poppy at the same time. This is a good example of why you should speak to your health care provider prior to taking California poppy.
Clonazepam (the family of diazepams) is basically a sedative. California poppy is a hypnotic and mild sedative. Therefore, taking both together will result in an additive effect.
Zyrtec is an antihistamine. There are no reported or theoretical interactions between Zyrtec and California poppy.
There are no reported or theoretical potential interactions between thyroid medication and California poppy.
In the case of green coffee or coffee, there are no reported interactions with the above medications.