Swedish bitters is said to have been formulated in a similar way to ancient bitters by Paracelsus and rediscovered by 18th century Swedish medics Dr. Klaus Samst and Dr. Urban Hjärne (which must be a mistake for his son Kristian Henrik Hjärne, who did invent a bitter).
In modern times Swedish bitters has been popularised by Maria Treben, an Austrian herbalist. The tonic is claimed to cure a large number of ailments and help digestion. However, these claims are presented with little in the way of scientific evidence to support them.
The alcoholic Swedish bitters is reported as having a similar flavour to Angostura bitters, though perhaps a little drier. Nowadays is more common to prepare Swedish bitters from a dry herbs mixture 
The following herbs are added to alcohol to make Swedish Bitters:
- aloe as active ingredient
- water extract of the following herbs:
- angelica root (angelica archangelica)
- carline thistle root (carlina acaulis)
- camphor (cinnamomum camphora)
- manna (fraxinus ornus)
- rhubarb root (rheum palmatum)
- senna (senna alexandrina)
- theriac venetian (theriac) (a mixture of many herbs and other substances)
- zedoary root (curcuma zedoaria)
Some Swedish Bitters that are sold might have up to 22 different ingredients. One of these Swedish Bitters is produced in Germany as a dry mix by Stefan Zwerenz, that consist of the following herbs:
1. Archangelica 2. Aloe Barbadensis 3. Lycopodiaceae 4. Pimpinella 5. Carlina acaulis 6. Veronicae herba 7. Althaea 8. Gentian lutea 9. Acorus calamus 10. Cinnamonum amphora 11. Kandis 12. Viscum album 13. Commiphora 14. Jugladaceae 15. Rhei radix 16. Carthamus tinctorius 17. Sennae folium 18. Ginkgo biloba 19. Theriaca 20. Potentilla erecta 21. Artemisia absinthium 22. Zedoariae rhizoma
More information and photos of these herbs can be found here Swedish Bitters by Stefan Zwerenz.