How do I set up a recursive, many-to-many relationship WITH an association class using JPA?

So I'm trying to create a pharmacy database that, among other things, keeps track of drug-to-drug interactions. I have a Drug entity with various members and associations and they all seem to work out fine thus far. The one implementation I'm not sure I have down correct is a recursive, many-to-many relationship with the Drug entity using an association class. The association class (DrugDrugIX) has 2 foreign keys - one from each drug - and a description and assignment of how severe is that interaction.

What I have so far works, in that it will compile and run and let me add Drugs and interactions. However, I certainly don't think what I'm doing is the most optimal -- or even correct. Any advice on how to optimize what I'm trying to do?

The Drug entity (some members omitted for brevity):

@Entity
@Table (name = "drugs")
@NamedQueries({
@NamedQuery (name = Drug.FIND_ALL_BY_NAME,
query = "SELECT d FROM Drug d WHERE LOWER (d.chemical_name) LIKE LOWER (CONCAT ('%', :searchString, '%'))" )
})
public class Drug
{
// QUERY STRING(S)
public static final String FIND_ALL_BY_NAME = "Drug.findAllByName";
@Id
@GeneratedValue (strategy = GenerationType.IDENTITY)
private long did;
private String chemical_name;
private String description;
// ASSOCIATION(S)
is this the correct implementation (???)
<----------------------------------------------------------------------------------->
@OneToMany (mappedBy = "base", cascade = CascadeType.PERSIST)
private List<DrugDrugIX> interxAsBase;
@OneToMany (mappedBy = "offender", cascade = CascadeType.PERSIST)
private List<DrugDrugIX> interxAsOffender;
<----------------------------------------------------------------------------------->
@ManyToOne (cascade = CascadeType.PERSIST)
private DEA_Class schedule;
@OneToOne (cascade = CascadeType.PERSIST)
private Pharmacology PK_profile;
(...) other associations, getters and setters here (...)
public void addInterxAsBase (DrugDrugIX interaction)
{
if (this.interxAsBase == null)
interxAsBase = new ArrayList<>();
interxAsBase.add (interaction);
}
public void addInterxAsOffender (DrugDrugIX interaction)
{
if (this.interxAsOffender == null)
interxAsOffender = new ArrayList<>();
interxAsOffender.add (interaction);
}
}

The DrugDrugIX association entity:

@Entity
@Table (name = "drug_drug_interactions")
public class DrugDrugIX
{
@EmbeddedId
private DrugDrugIX_PK interaction_CPK;
private int severityLevel = -1;
// ASSOCIATION(S)
@ManyToOne
@MapsId ("base")
private Drug base;
@ManyToOne
@MapsId ("offender")
private Drug offender;
(...) getters, setters omitted for brevity (...)
public void registerInteraction (Drug object, Drug precipitate)
{
if (this.base == null)
this.base = object;
if (this.offender == null)
this.offender = precipitate;
if ((this.base == object && this.offender == precipitate) && (severityLevel == -1))
{
object.addInterxAsBase(this);
precipitate.addInterxAsOffender(this);
}
}
}

...and just for posterity, the Embeddable that comprises the primary key of the DrugDrugIX entity:

@Embeddable
public class DrugDrugIX_PK implements Serializable
{
private long base;
private long offender;
private String description;
// CONSTRUCTORS
public DrugDrugIX_PK () {}
public DrugDrugIX_PK (Drug base, Drug offender, String description)
{
this.base = base.getDID();
this.offender = offender.getDID();
this.description = description;
}
// ACCESSORS
public String getDescription () { return this.description; }
// MISCELLANEOUS
@Override
public boolean equals (Object other)
{
if (other instanceof DrugDrugIX_PK)
{
DrugDrugIX_PK second = (DrugDrugIX_PK) other;
return (this.base == second.base) && (offender == second.offender) && (this.description.equals (description));
}
else
return false;
}
@Override
public int hashCode () { return (int) (base + offender); }
}

I pray to the stackoverflow gods for guidance..

You do not need to use recursion. Just use two nested loops. Something like this pseudo code:

int[] drugs = {1, 4, 6};
for (i=0; i<drugs.length; i++) {
drug1 = drugs[i];
for (int j=i+1; j<drugs.length; j++) {
drug2 = drugs[j];
get_interaction(drug1, drug2);
}
}

Drugs being administered are represented by integers in the drugs array.