One’s study of the Materia Medica is never complete unless one studies the remedy relationship of the drugs. Drosera is one such drug. The modalities in Drosera < after midnight and in Spongia < before midnight is the key differentiation between this two remedies. However, many of us are not aware of the fact that the drug that is complementary to Drosera is Nux vomica. You may confirm this by opening even the so-called “simple” book of Materia Medica- Allen’s Keynotes and see this in the relationship section of Drosera. I would now like to direct your attention to Kent’s repertory. Open the Cough chapter and go to the rubric DRY. If you go to the sub rubric night and follow it to midnight, you will come across an entry: midnight after, daybreak until. One would be tempted to make a wild guess and think that the drug listed will be Drosera. However to your surprise you will find only one drug and that too in bold- Nux vomica! The two sub rubrics under this are also interesting and important:  lying on back agg. - Nux vom; lying on side amel.- Nux vom.This exercise in rubric hunting was just a reminder to you that the Materia Medica and the Repertory complement each other and that we can also use the Repertory efficiently to  study the Materia Medica.
It must be noted that the cough of Drosera is productive and often associated with haemoptysis (Tubercular miasm) while the cough of Nux vomica is dry and spasmodic from simple inflammation (Psoric miasm). [This shows that the knowledge of homoeopathic philosophy is also very important for the study of Materia Medica.]

     
    A 65-year-old lady presented with dry cough since 1 month. Cough < night especially 2.00am and as soon she touches the pillow. Patient is a known case of diabetes and hypertension. Cough every year during October-December since 4 years. Based on totality,Drosera 200 three doses were prescribed. Patient was kept under observation without any medicine for one year. This year patient reported to me after one year that he did not have any complaints.

     
  I have used in many cases with irritating continuous cough in children who have night aggravation. In many cases this remedy had helped when Rumex and Spongia failed.